1. Field of the Invention
The present invention relates to the operation of large engines such as natural gas engines using additized lubricating oil formulations.
2. Description of the Related Art
Natural gas fueled engines are typically four-stroke spark-ignited engines having 12 to 20 cylinders or more similar to heavy duty diesel engines. The engines are typically deployed in the gas and oil industry to compress natural gas at the well heads and along the pipeline. Another common application is distributed power generation or combined heating and power (CHP). Due to the nature of this latter application, the engines fueled by natural gas run continuously near full load conditions, shutting down only for maintenance or oil changes. Higher energy costs result in higher operating costs and create a strong driver for customers to improve the efficiency of their natural gas engine operations. Based on today's natural gas fuel prices, fuel efficiency gains of 1-4% for a typical 1000 bhp gas engine can yield considerable annual savings per engine. In addition, less fuel is burned; proportionately less CO2 (greenhouse gas) is produced.
Because the lubricant is subjected to a constant high temperature environment, the life of the lubricant is often limited by its oxidation stability. Moreover, because natural gas-fired engines run with high emission of nitrogen oxides (NOx), the lubricant life may also be limited by its nitration resistance. A longer term requirement is that the lubricant must also maintain cleanliness within the high temperature environment of the engine, especially for critical components such as bearings, cylinder walls, pistons and piston rings. Therefore, it is desirable for gas engine oils to have good cleanliness qualities while promoting long life through enhanced resistance to oxidation and nitration.
Gas engine oil of enhanced life as evidenced by an increase in the resistance of the oil to oxidation, nitration and deposit formation is the subject of U.S. Pat. No. 5,726,133. The gas engine oil of that patent is a low ash gas engine oil comprising a major amount of a base oil of lubricating viscosity and a minor amount of an additive mixture comprising a mixture of detergents comprising at least one alkali or alkaline earth metal salt having a Total Base Number (TBN) of about 250 and less and a second alkali or alkaline earth metal salt having a TBN lower than the aforesaid component. The TBN of this second alkali or alkaline earth metal salt will typically be about half or less that of the first component.
The fully formulated gas engine oil of U.S. Pat. No. 5,726,133 can also typically contain other standard additives known to those skilled in the art, including dispersants (about 0.5 to 8 vol %), phenolic or aminic anti-oxidants (about 0.05 to 1.5 vol %), metal deactivators such as triazoles, alkyl-substituted dimercaptothiadiazoles (about 0.01 to 0.2 vol %), anti-wear additives such as metal dithiophosphates, metal dithiocarbamates, metal xanthates or tricresylphosphates (about 0.05 to 1.5 vol %), pour point depressants such as poly (meth) acrylates or alkyl aromatic polymers (about 0.05-0.6 vol %), anti-foamants such as silicone anti-foaming agents (about 0.005 to 0.15 vol %) and viscosity index improvers, such as olefin copolymers, polymethacrylates, styrene-diene block copolymers, and star copolymers (up to about 15 vol %, preferably up to about 10 vol %).
U.S. Pat. No. 6,191,081 is directed to a lubricating oil composition for natural gas engines comprising a major amount of a base oil of lubricating viscosity and a minor amount of a mixture of one or more metal salicylate detergents and one or more metal phenate and/or metal sulfonate detergents.
The lubricating oil base stock is any natural or synthetic lubricating base oil stock fraction typically having a kinematic viscosity at 100° C. of about 5 to 20 cSt. In a preferred embodiment, the use of a viscosity index improver permits the omission of oil of viscosity about 20 cSt or more at 100° C. from the lube base oil fraction used to make the formulation. Therefore, a preferred base oil is one which contains little, if any, heavy fraction; e.g., little, if any, lube oil fraction of viscosity 20 cSt or higher at 100° C.
The lubricating oil base stock can be derived from natural lubricating oils, synthetic lubricating oils or mixtures thereof. Suitable base stocks include those in API categories I, II and III, where saturates level and Viscosity Index are:                Group I—less than 90% and 80-120, respectively;        Group II—greater than 90% and 80-120, respectively; and        Group III—greater than 90% and greater than 120, respectively.        
Suitable lubricating oil base stocks also include base stocks obtained by isomerization of synthetic wax and slack wax, as well as hydrocrackate base stocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude.
The mixture of detergents comprises a first metal salt or group of metal salts selected from the group consisting of one or more metal sulfonates(s), salicylate(s), phenate(s) and mixtures thereof having a high TBN of greater than about 150 to 300 or higher, a second metal salt or group of metal salts selected from the group consisting of one or more metal salicylate(s), metal sulfonate(s), metal phenate(s) and mixtures thereof having a medium TBN of greater than about 50 to 150, and a third metal salt or group of metal salts selected from the group consisting of one or more metal sulfonate(s), metal salicylate(s) and mixtures thereof identified as neutral or low TBN, having a TBN of about 10 to 50, the total amount of medium plus neutral/low TBN detergent being about 0.7 vol % or higher (active ingredient) wherein at least one of the medium or low/neutral TBN detergent(s) is metal salicylate, preferably at least one of the medium TBN detergent(s) is a metal salicylate. The total amount of high TBN detergents is about 0.3 vol % or higher (active ingredient). The mixture contains salts of at least two different types, with medium or neutral salicylate being an essential component. The volume ratio (based on active ingredient) of the high TBN detergent to medium plus neutral/low TBN detergent is in the range of about 0.15 to 3.5.
The mixture of detergents is added to the lubricating oil formulation in an amount up to about 10 vol % based on active ingredient in the detergent mixture, preferably in an amount up to about 8 vol % based on active ingredient, more preferably 6 vol % based on active ingredient in the detergent mixture, most preferably between about 1.5 to 5.0 vol %, based on active ingredient in the detergent mixture. Preferably, the total amount of metal salicylate(s) used of all TBNs is in the range of between 0.5 vol % to 4.5 vol %, based on active ingredient of metal salicylate, the combination of the recited metal salts per se or in combination with any additional metal salts or groups of metal salts being used in an amount sufficient to produce a lubricating oil of at least 0.65 wt % sulfated ash content.
U.S. Published Application US2005/0059563 is directed to a lubricating oil composition, automotive gear lubricating composition and fluids useful in the preparation of finished automotive gear lubricants and gear oils comprising a blend of a PAO having a viscosity of between about 40 cSt (mm2/s) and 1000 cSt (mm2/s) @ 100° C., and an ester having a viscosity of less than or equal to about 2.0 cSt (mm2/s) @ 100° C. wherein the blend of PAO and ester has a viscosity index greater than or equal to the viscosity index of the PAO. The composition may further contain thickeners, anti-oxidants, inhibitor packages, anti-rust additives, dispersants, detergents, friction modifiers, traction improving additives, demulsifiers, defoamants, dyes and haze inhibitors.
U.S. Published Application US2003/0191032 is directed to a detergent additive for lubricating oil compositions comprising at least two of low, medium and high TBN detergents, preferably a calcium salicylate. The detergent is in a lubricating oil composition comprising at least one of Group II base stock, Group III base stock or wax isomerate base stock and mixtures thereof, and an optional minor quantity of a co-base stock(s). Co-base stocks include polyalpha olefin oligomeric low and medium and high viscosity oil, di-basic acid esters, polyol esters, other hydrocarbon oils, supplementary hydrocarbyl aromatics and the like.
US Published Application 2006/0276355 is directed to a lubricant blend for enhanced micropitting properties wherein the lubricant comprises at least two base stocks with a viscosity difference between the first and second base stock of greater than 96 cSt (mm2/s) @ 100° C. At least one base stock is a polyalpha olefin with a viscosity of less than 6 mm2/s but greater than 2 cSt (mm2/s), and the second base stock is a synthetic oil with a viscosity greater than 100 cSt (mm2/s) but less than 300 cSt (mm2/s) @ 100° C. The second base stock can be a high viscosity polyalpha olefin.
U.S. Published Application 2007/0289897 is directed to a lubricating oil blend comprising at least two base stocks with a viscosity difference between the first and second base stock of greater than 96 cSt (mm2/s) @ 100° C., the lubricant exhibiting improved air release. The blend contains at least one synthetic PAO having a viscosity of less than 10 cSt (mm2/s) but greater than 2 cSt (mm2/s) @ 100° C. and a second synthetic oil having a viscosity greater than 100 cSt (mm2/s) but less than 300 cSt (mm2/s) @ 100° C. The lubricant can contain anti-wear, anti-oxidant, defoamant, demulsifier, detergent, dispersant, metal passivator, friction reducer, rust inhibitor additive and mixtures thereof.
U.S. Published Application 2007/0298990 is directed to a lubricating oil comprising at least two base stocks, the first base stock has a viscosity greater than 40 cSt (mm2/s) @ 100° C. and a molecular weight distribution (MWD) as a function of viscosity at least 10% less than algorithm:MWD=0.2223+1.0232*log(Kv at 100° C. in cSt)and a second base stock with a viscosity less than 10 cSt (mm2/s) @ 100° C. Preferably the difference in viscosity between the first and second stocks is greater than 30 cSt (mm2/s) @ 100° C. Preferably the higher viscosity first stock is a metallocene catalyzed PAO base stock. The second stock can be selected from GTL lubricants, wax-derived lubricants, PAO, brightstock, brightstock with PIB, Group I base stocks, Group II base stocks, Group III base stocks and mixtures thereof. The lubricant can contain additives including detergents. Preferably the first stock has a viscosity of greater than 300 cSt (mm2/s) @ 100° C., the second stock has a viscosity of between 1.5 cSt (mm2/s) to 6 cSt (mm2/s) @ 100° C. Preferably the difference in viscosity between the first and second stocks is greater than 96 cSt (mm2/s) @ 100° C.
U.S. Published Application US2008/0207475 is directed to a lubricating oil comprising at least two base stocks, the first base stock having a viscosity of at least 300 cSt (mm2/s) @ 100° C. and a molecular weight distribution (MSD) as a function of viscosity at least 10% less than algorithm:MWD=0.2223+1.0232*log(KV @ 100° C. in cSt)and the second stock has a viscosity of less than 100 cSt (mm2/s) @ 100° C. Preferably the difference in viscosity between the first and second stocks is greater than 250 cSt (mm2/s) @ 100° C. Preferably the first stock is a metallocene catalyzed PAO base stock. The second stock can be chosen from GTL base stock, wax-derived base stock, PAO, brightstock, brightstock with PIB, Group I base stock, Group II base stock, Group III base stock, Group V base stock, Group VI base stock and mixtures thereof. The lubricant can contain additives including detergents.
U.S. Pat. No. 6,140,281 is directed to long life gas engine lubricating oils containing detergents. The lubricating oil comprises a major amount of a base oil of lubricating viscosity and a minor amount of a mixture of one or more metal sulfonate(s) and/or phenate(s) and one or more metal salicylate(s) detergents, all detergents in the mixture having the same or substantially the same Total Base Number (TBN).
The lubricating oil base stock is any natural or synthetic lubricating base stock fraction typically having a kinematic viscosity at 100° C. of about 5 to 20 cSt (mm2/s), more preferably about 7 to 16 cSt (mm2/s), most preferably about 9 to 13 cSt (mm2/s). In a preferred embodiment, the use of a viscosity index improver permits the omission of oil of viscosity 20 cSt (mm2/s) or more at 100° C. from the lube base oil fraction used to make the formulation. Therefore, a preferred base oil is one which contains little, if any, heavy fractions; e.g., little, if any, lube oil fraction of viscosity 20 cSt (mm2/s) or higher at 100° C.
The lubricating oil base stock can be derived from natural lubricating oils, synthetic lubricating oils or mixtures thereof. Suitable base stocks include those in API categories I, II and III, where saturates level and Viscosity Index are:                Group I—less than 90% and 80-120, respectively;        Group II—greater than 90% and 80-120, respectively; and        Group III—greater than 90% and greater than 120, respectively.        
Suitable lubricating oil base stocks include base stocks obtained by isomerization of synthetic wax and slack wax, as well as hydrocrackate base stocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude.
The detergent is a mixture of one or more metal sulfonate(s) and/or metal phenate(s) with one or more metal salicylate(s). The metals are any alkali or alkaline earth metals; e.g., calcium, barium, sodium, lithium, potassium, magnesium, more preferably calcium, barium and magnesium. It is a feature of the lubricating oil that each of the metal salts used in the mixture.
The TBNs of the salts will differ by no more than about 15%, preferably no more than about 12%, more preferably no more than about 10% or less.
The one or more metal sulfonate(s) and/or metal phenate(s), and the one or more metal salicylate(s) are utilized in the detergent as a mixture, for example, in a ratio by parts of 5:95 to 95:5, preferably 10:90 to 90:10, more preferably 20:80 to 80:20.
The mixture of detergents is added to the lubricating oil formulation in an amount up to about 10 vol % based on active ingredient in the detergent mixture, preferably in an amount up to about 8 vol % based on active ingredient.
U.S. Pat. No. 6,645,922 is directed to a lubricating oil for two-stroke cross-head marine diesel engines comprising a base oil and an oil-soluble overbased detergent additive in the form of a complex wherein the basic material of the detergent is stabilized by more than one surfactant. The more than one surfactants can be mixtures of: (1) sulfurized and/or non-sulfurized phenols and one other surfactant which is not a phenol surfactant; or (2) sulfurized and/or non-sulfurized salicylic acid and one other surfactant which is not a salicylic surfactant; or (3) at least three surfactants which are sulfurized or non-sulfurized phenol, sulfurized or non-sulfurized salicylic acid and one other surfactant which is not a phenol or salicylic surfactant; or (4) at least three surfactants which are sulfurized or non-sulfurized phenol, sulfurized or non-sulfurized salicylic acid and at least one sulfuric acid surfactant.
The base stock is an oil of lubricating viscosity and may be any oil suitable for the system lubrication of a cross-head engine. The lubricating oil may suitably be an animal, vegetable or a mineral oil. Suitably the lubricating oil is a petroleum-derived lubricating oil, such as naphthenic base, paraffinic base or mixed base oil. Alternatively, the lubricating oil may be a synthetic lubricating oil. Suitable synthetic lubricating oils include synthetic ester lubricating oils, which oils include diesters such as di-octyl adipate, di-octyl sebacate and tri-decyl adipate, or polymeric hydrocarbon lubricating oils, for example, liquid polyisobutene and polyalpha olefins. Commonly, a mineral oil is employed. The lubricating oil may generally comprise greater than 60% by mass, typically greater than 70% by mass of the lubricating oil composition and typically have a kinematic viscosity at 100° C. of from 2 to 40 cSt (mm2/s), for example, from 3 to 15 cSt (mm2/s), and a viscosity index from 80 to 100, for example, from 90 to 95.
Another class of lubricating oil is hydrocracked oils, where the refining process further breaks down the middle and heavy distillate fractions in the presence of hydrogen at high temperatures and moderate pressures. Hydrocracked oils typically have kinematic viscosity at 100° C. of from 2 to 40 cSt (mm2/s), for example, from 3 to 15 cSt (mm2/s), and a viscosity index typically in the range of from 100 to 110, for example, from 105 to 108.
Brightstock refers to base oils which are solvent-extracted, de-asphalted products from vacuum residuum generally having a kinematic viscosity at 100° C. from 28 to 36 cSt (mm2/s), and are typically used in a proportion of less than 30, preferably less than 20, more preferably less than 15, most preferably less than 10, such as less than 5 mass %, based on the mass of the lubricating oil composition.
U.S. Pat. No. 6,613,724 is directed to gas fueled engine lubricating oils comprising an oil of lubricating viscosity, a detergent including at least one calcium salicylate having a TBN in the range 70 to 245, 0 to 0.2 mass % of nitrogen, based on the mass of the oil composition, of a dispersant and minor amounts of one or more co-additive. The base oil can be any animal, vegetable, mineral oil or synthetic oil. The base oil is used in a proportion of greater than 60 mass % of the composition. The oil typically has a viscosity at 100° C. of from 2 to 40 cSt (mm2/s), for example 3 to 15 cSt (mm2/s) and a viscosity index of from 80 to 100. Hydrocracked oils can also be used which have viscosities of 2 to 40 cSt (mm2/s) at 100° C. and viscosity indices of 100 to 110. Brightstock having a viscosity at 100° C. of from 28 to 36 cSt (mm2/s) can also be used, typically in a proportion less than 30, preferably less than 20, most preferably less than 5 mass %.
U.S. Pat. No. 7,101,830 is directed to a gas engine oil having a boron content of more than 95 ppm comprising a major amount of a lubricating oil having a viscosity index of 80 to 120, at least 90 mass % saturates, 0.03 mass % or less sulfur and at least one detergent. Metal salicylate is a preferred detergent.
U.S. Pat. No. 4,956,122 is directed to a lubricating oil composition containing a high viscosity synthetic hydrocarbon such as high viscosity PAO, liquid hydrogenated polyisoprenes, or ethylene-alpha olefin copolymers having a viscosity of 40-1000 cSt (mm2/s) at 100° C., a low viscosity synthetic hydrocarbon having a viscosity of between 1 and 10 cSt (mm2/s) at 100° C., optionally a low viscosity ester having a viscosity of between 1 and 10 cSt (mm2/s) at 100° C. and optionally up to 25 wt % of an additive package.